CN108411368B - A fast and selective method for reducing the density of micropipes and dislocations in SiC crystals - Google Patents

Abstract

The invention relates to a method for rapidly and selectively reducing the density of micropipes and dislocations in SiC crystals. The invention utilizes a SiC region with a density of micropipes <1 cm ^-2 and a dislocation density less than or equal to 5000 cm ^-2 to cover the micropipes and the dislocation density. High dislocation density region, thereby blocking the extension of dislocations and microtubules, effectively reducing the inheritance of dislocations and microtubules, and obtaining SiC bulk single crystals with specific microtubule and dislocation densities, with high selectivity It is possible to obtain bulk single crystals with low microtubules and dislocations by only one growth, greatly shortening the optimization time.

Description

A fast and selective method for reducing the density of micropipes and dislocations in SiC crystals

technical field

The invention relates to a method for rapidly and selectively reducing the density of micropipes and dislocations in SiC crystals, belonging to the technical field of crystal growth.

Background technique

As a third-generation semiconductor material, SiC single crystal material has excellent electrical properties including wide band gap, high thermal conductivity, high electron saturation mobility, and high breakdown electric field. Ideal semiconductor material for power electronic devices, it is widely used in white light lighting, optical storage, screen display, aerospace, high temperature radiation environment, oil exploration, automation, radar and communication, automotive electronics, etc. The most successful and commercial method for growing SiC crystals is still the physical vapor transport (PVT) method.

With the gradual improvement of the quality of SiC single crystal, the diameter of SiC is getting larger and larger, and the defect density is getting smaller and smaller. For SiC growers, although the density of microtubes is effectively controlled. However, the SiC material itself still has the problem of relatively high dislocation density. The dislocation density is generally 103-105cm ^-2 . For the device, the existence of dislocation reduces the performance of the device and affects the long-term reliability.

More and more researches focus on the formation mechanism of defects and find ways to reduce the defect density. DaisukeNakamura et al. proposed repeating the a-plane to obtain micropipette-free ultra-low dislocation SiC single crystals. But this method requires multiple growths to obtain. J.Li et al. proposed that a crystal with zero micropipes can be obtained by (01-14) plane growth, but the crystal diameter obtained is small and cannot be compared with commercial 2-6inch single crystals. Sakwe Aloysius Sakwe et al. discuss the effect of N and P-type doping on dislocation density. Although the dislocation density distribution can be changed by doping, the dislocation density cannot be reduced.

It can be seen that there is still no effective way to improve the quality of SiC single crystal and reduce the density of micropipes and dislocations at this stage. Therefore, it is very necessary to provide a fast and selective crystalline method for reducing the density of micropipes and dislocations in SiC crystals.

SUMMARY OF THE INVENTION

Aiming at the deficiencies of the prior art, the present invention provides a method for rapidly and selectively reducing the density of micropipes and dislocations in SiC crystals.

The technical scheme of the present invention is as follows:

A method for rapidly and selectively reducing the density of micropipes and dislocations in SiC crystals, comprising the following steps:

(1) Select a SiC region with a micropipe density <1cm ^-2 and a dislocation density less than or equal to 5000cm ^-2 , and cut it into a symmetrical crystal with a polar surface on the side;

(2) fixing the symmetrical crystal cut in step (1) in the multi-microtube multi-dislocation region of the SiC seed crystal;

(3) The SiC seed crystal treated in step (2) is subjected to two-stage crystal growth. The first stage: low temperature and low pressure promote lateral growth, forming a full-chip micropipe density <5cm ^-2 , dislocation density <5000cm ^-2 The complete seed crystal of , the second stage: growth using approximate equilibrium growth conditions.

Preferably according to the present invention, the crystal form of the crystal in step (1) is consistent with the crystal form of the SiC seed crystal in step (2).

Preferably according to the present invention, in step (1), the micropipe density of the crystal is <0.1 cm ⁻² , and the dislocation density is less than or equal to 10 ³ cm ⁻² .

Preferably according to the present invention, the crystals cut in step (1) are crystals with 3 times and 6 times symmetry, the side faces are polar faces, and the polar faces are (1-100) and/or (11-20) noodle.

Preferably according to the present invention, the cut crystals in step (1) are annealed at high temperature or polished to remove the cut damage layer.

Preferably according to the present invention, in step (2), the SiC seed crystal is a seed crystal larger than 4 inches, and the crystal form is 4H, 6H, 3C or 15R.

Further preferably, the SiC seed crystal is a 4-inch seed crystal, a 6-inch seed crystal, an 8-inch seed crystal or a 16-inch seed crystal.

According to a preferred embodiment of the present invention, in step (2), the fixing method is fixed by means of graphite glue or metal coating.

Preferably according to the present invention, in step (3), the low temperature and low pressure growth is: 200-400°C lower than the growth temperature and the pressure is 0.1-30mbar, and the growth time is 2-20h.

Further preferably, the low temperature and low pressure growth temperature is 1700-2200° C., the pressure is 0.5-5 mbar, and the growth time is 8-10 h.

Preferably according to the present invention, in step (3), the lateral growth rate is greater than 8um/h, and the axial growth rate in the seed crystal treatment stage is less than 60um/h.

Further preferably, in step (3), the lateral growth rate is 10-20um/h, and the axial growth rate in the seed crystal treatment stage is 40-50um/h.

Preferably according to the present invention, in step (3), the approximate equilibrium growth conditions are that the temperature difference between the source material and the seed crystal is less than 100°C; and the pressure is 5-15 mbar.

Further preferably, the approximate equilibrium growth conditions are that the temperature difference between the source material and the seed crystal is 60-80° C.; and the pressure is 8-12 mbar.

Preferably according to the present invention, the growth method of step (3) is PVT, HTCVD or liquid phase growth method.

Principle of the present invention:

Dislocations and micropipes are typical structural defects in SiC single crystals. Based on Frank's theory, micropipes are considered to be dislocations with large Burgers vectors. In SiC growth, dislocations and micropipes extend along the [0001] direction. During growth along the (001) plane, microtubules and dislocations will extend from the seed crystal into the crystal, resulting in the inheritance of microtubules and dislocations from the seed crystal to the bulk crystal. The present invention utilizes microtubule densities < 1 cm ^-2 , The SiC area with dislocation density less than or equal to 5000cm ^-2 covers microtubules and areas with high dislocation density, thereby blocking the extension of dislocations and microtubules, and effectively reducing the inheritance of dislocations and microtubules. The invention can selectively optimize the single crystal quality, and can obtain bulk crystals with low micropipes and low dislocations only through one-time growth.

Beneficial effects of the present invention:

1. The present invention uses the SiC region with micropipe density <1cm ^-2 and dislocation density less than or equal to 5000cm ^-2 to cover micropipes and areas with high dislocation density, thereby blocking the extension of dislocations and micropipes and effectively reducing the dislocation density. The inheritance of dislocations and microtubules is reduced, and SiC bulk single crystals with specific microtubule and dislocation densities can be obtained with high selectivity.

2. The method of the present invention can obtain a bulk single crystal with low micropipes and dislocations by only one growth, which greatly shortens the optimization time.

3. The method of the present invention is particularly helpful for improving the local quality of the SiC substrate with a diameter of more than 100 mm, and improving the growth efficiency of the large-diameter substrate.

Description of drawings

1 is a schematic diagram of a growth chamber structure for growing SiC crystals by physical vapor transport (PVT) method in Experimental Example 1;

1. Graphite fiber insulation layer, 2. The gap between the upper insulation material and the top of the crucible, 3. The seed crystal, 4. The crucible, 5. The gap between the side insulation material and the side wall of the crucible, 6. The source material powder.

Figure 2 is a schematic diagram of the multi-microtube distribution structure of the SiC substrate before being optimized;

Fig. 3 is a schematic structural diagram of covering the higher region of the micropipes by using the SiC region with the density of micropipes <1cm ^-2 and the dislocation density less than or equal to 5000cm ^-2 ;

FIG. 4 is a schematic diagram of the micropipe distribution structure of the optimized 150mm SiC seed crystal.

Detailed ways

The present invention will be further illustrated by the following examples, but the present invention is not limited to the following examples.

Example 1:

A method for rapidly and selectively reducing the density of micropipes and dislocations in SiC crystals, comprising the following steps:

(1) Select the SiC region of the crystal with micropipe density <0.1cm ^-2 and dislocation density ≤10 ³ cm ^-2 , and cut it into a 6-order symmetric crystal whose side is a polar plane, and the cut crystal is polished to remove the damage of cutting Floor;

(2) the symmetrical crystal processed in step (1) is fixed in the multi-microtube multi-dislocation region of the SiC seed crystal by using graphite glue, and the crystal form of the crystal in step (1) is the same as that of the SiC seed crystal in step (2). consistent;

(3) The SiC seed crystal treated in step (2) is subjected to two-stage crystal growth. The first stage: low temperature and low pressure promote lateral growth, the low temperature and low pressure growth temperature is 1700 ° C, the pressure is 1 mbar, and the growth time is 10 h; A complete seed crystal with microtube density <5cm ^-2 and dislocation density <5000cm ^-2 is obtained, the lateral growth rate is 15um/h, and the axial growth rate in the seed crystal treatment stage is 50um/h; the second stage: using The approximate equilibrium growth conditions were used for growth; the approximate equilibrium growth conditions were that the temperature difference between the source material and the seed crystal was 80° C.; and the pressure was 12 mbar.

Specific experimental example:

Aiming at the problem that the current large-size SiC crystal has a long R&D period to optimize and improve the quality, and it is difficult to reduce the density of micropipes and dislocations, this experimental example is based on the method of growing SiC single crystal by physical vapor transport technology, and the method of Example 1 is used to obtain high-quality SiC crystal rod.

In the experimental example, the structure of the growth chamber for growing SiC crystals by physical vapor transport (PVT) method is shown in Figure 1. A crucible is arranged in the growth chamber, the bottom of the crucible is filled with source material powder, the seed crystal is fixed on the crucible cover, and the growth chamber is The exterior is provided with a graphite fiber thermal insulation layer.

The seed crystal 9 is a 6-inch, 4HSiC substrate material; using the micro-pipe testing method, the micro-pipe distribution is obtained as shown in FIG. 2 . There are two microtubule aggregation areas, concentrated in the range of ²⁰ *30cm2 and 40*40cm2.

The 3inch4H-SiC single crystal substrate material is selected, the micropipe density is less than 0.5cm ^-2 and the dislocation density is 2000cm ^-2 . Cut into 6-order symmetric crystals whose sides are polar planes, that is, in Figure 3, 7 and 8, whose edges are all (1-100) planes. Regions 7 and 8 were annealed at 1500° and polished to remove the damaged layer. Use carbon glue to fix the 150mm seed crystal 9 in the area that needs to be optimized.

The crystal is grown by physical vapor transport technology, and the first step of growth is carried out. The growth temperature is 1850 ° C, the pressure is 4 mbar, and the mixed gas of argon and nitrogen is used as the carrier gas to promote lateral growth and form a complete seed crystal. Then the temperature was raised to the growth temperature, 2200°C, and 100mbar was used for SiC single crystal growth. After the growth is completed, cut and measure the optimized micropipe distribution; the micropipe distribution structure of the optimized 150mm SiC seed crystal is shown in Figure 4, which effectively reduces the micropipes, and can obtain a low-micropipe bulk unit in one growth. It can greatly shorten the optimization time, improve the local quality of SiC substrates with a diameter of 150mm, and improve the growth efficiency of large-diameter substrates.

Example 2:

A method for rapidly and selectively reducing the density of micropipes and dislocations in SiC crystals, comprising the following steps:

(1) Select the SiC region of crystal with micropipe density <0.1cm ^-2 and dislocation density ≤10 ³ cm ^-2 , and cut it into a 3-order symmetric crystal whose side is a polar plane, and the cut crystal is polished to remove the damage of cutting Floor;

(2) the symmetrical crystal processed in step (1) is fixed in the multi-microtube multi-dislocation region of the SiC seed crystal by using graphite glue, and the crystal form of the crystal in step (1) is the same as that of the SiC seed crystal in step (2). consistent;

(3) The SiC seed crystal processed in step (2) is subjected to two-stage crystal growth. The first stage: low temperature and low pressure promote lateral growth, the low temperature and low pressure growth temperature is 1900 ° C, the pressure is 2 mbar, and the growth time is 8 h; A complete seed crystal with microtube density <5cm ^-2 and dislocation density <5000cm ^-2 is obtained, the lateral growth rate is 20um/h, and the axial growth rate in the seed crystal treatment stage is 40um/h; the second stage: using The approximate equilibrium growth conditions were used for growth; the approximate equilibrium growth conditions were that the temperature difference between the source material and the seed crystal was 60° C.; and the pressure was 12 mbar.

Claims (9)

1. A method for rapidly and selectively reducing the density of micropipes and dislocations in a SiC crystal, comprising the steps of: (1) Select a SiC region with a density of micropipes <1cm ^-2 and a dislocation density of less than 5000cm ^-2 , and cut it into a symmetrical crystal with polar planes on the sides; (2) Fixing the symmetrical crystal cut in step (1) in the multi-microtube multi-dislocation region of the SiC seed crystal; (3) The SiC seed crystal treated in step (2) is subjected to two-stage crystal growth. The first stage: low temperature and low pressure promote lateral growth, forming a full-chip micropipe density <5cm ^-2 and dislocation density <5000cm ^-2 The complete seed crystal, the second stage: use the approximate equilibrium growth conditions for growth; the approximate equilibrium growth conditions are that the temperature difference between the source material and the seed crystal is 60-80 ° C; the pressure is 8-12 mbar. 2. The method for rapidly and selectively reducing the density of micropipes and dislocations in a SiC crystal according to claim 1, wherein the crystal form of the crystal in step (1) is the same as the crystal form of the SiC seed crystal in step (2). The microtubule density of the crystal is <0.1cm ^-2 , and the dislocation density is less than or equal to 10 ³ cm ^-2 . 3 . The method for rapidly and selectively reducing the density of micropipes and dislocations in SiC crystals according to claim 1 , wherein the crystals cut in step (1) are crystals with 3 times and 6 times symmetry , the side surface is the polar surface, and the polar surface is the (1-100) or (11-20) surface; the cut crystal is annealed at high temperature or polished to remove the cut damage layer. 4. The method for rapidly and selectively reducing the density of micropipes and dislocations in SiC crystals according to claim 1, wherein in step (2), the SiC seed crystal is a seed crystal larger than 4 inches, and the crystal form is 4H, 6H, 3C or 15R. 5 . The method for rapidly and selectively reducing the density of micropipes and dislocations in SiC crystals according to claim 1 , wherein in step (2), the fixing method adopts the method of graphite glue or metal coating. 6 . to be fixed. 6 . The method for rapidly and selectively reducing the density of micropipes and dislocations in SiC crystals according to claim 1 , wherein in step (3), the low-temperature and low-pressure growth is: 200-400°C lower than the growth temperature. 7 . ℃, the pressure is 0.1-30mbar, the growth time is 2-20h. 7. The method for rapidly and selectively reducing the density of micropipes and dislocations in SiC crystals according to claim 6, wherein the low-temperature and low-pressure growth temperature is 1700-2200° C., the pressure is 0.5-5 mbar, and the growth time is 8-10h. 8. The method for rapidly and selectively reducing the density of micropipes and dislocations in SiC crystals according to claim 1, wherein in step (3), the lateral growth rate is greater than 8um/h, and the seed crystal treatment stage The axial growth rate is less than 60um/h. 9 . The method for rapidly and selectively reducing the density of micropipes and dislocations in SiC crystals according to claim 8 , wherein in step (3), the lateral growth rate is 10-20um/h, and the seed crystal The axial growth rate in the treatment phase was 40-50 um/h.

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